As one approach toward identifying the protein products of the F factor transfer operon, membrane proteins of mutant male strains are being examined. One protein associated with the surface exclusion region of the tra operon has already been identified. In addition a lambda-F transducing phage has been constructed which carries complementing activity for traJ. The protein products made by this phage in UV irradiated hosts are being examined by slab gel electrophoresis. Construction of additional phages carrying other tra activities is also being attempted.